I have seen two stage productions of The Phantom of the Opera (and there have been at least four). As a result, I became curious about the original novel by Gaston Leroux. So during my recent trip to Germany I downloaded it to my Kindle and read it during the long plane rides.
Of course, a novel and a theatrical production are completely different media, so the story is going to be adjusted accordingly. But it’s interesting to compare. If you’ve never read the book, it’s a very worthwhile read, and there are free Kindle editions on Amazon.com. Andrew Lloyd Webber’s musical is great in its own right, but reduces the story to its bare essentials. If you’re big on story, you’ll need the novel to fill in the gaps. I’ll just say the Phantom has a very interesting past, and there are reasonably logical explanations for the mysterious happenings in the opera house.
Gaston Leroux also wrote The Mystery of the Yellow Room and The Perfume of the Lady in Black. Perhaps someday I’ll get a chance to read them, too. And now I’m curious about The Hunchback of Notre Dame.
Also see https://en.wikipedia.org/wiki/The_Phantom_of_the_Opera